I am using Ubuntu 16.04 LTS (very happy with it so far), but I am facing a really weird issue. It's not impossible that I have changed a setting somewhere to break it, but I cannot find such a setting anywhere.
When I launch the Files application (Nautilus) I do not see the application in the launcher (the left panel). When I Alt+Tab I see all other apps (except minimized), but Files is also missing. The app is not minimized.